what does ip connection error in FortiAnalyzer mean?

greetings all,

I'd like to know what does "IP connection error" exactly mean in FortiAnalyzer? 

we are a production factory and when there is some delay from the production line, I can see the log IP connection error displayed in fortianalyzer, and matches the production delay time. So it is quite critical that we know what does this exactly mean, so we have a direction to do troubleshooting.

is this log entry a single packet? or it consists of a complete 3-way handshake of a TCP connection or even more? What could cause the kind of log occur?

If the log detail is needed, please see the screenshot as below: